I. Field of the Invention
This invention relates generally to high speed pick-and-place robotic machines, and more particularly to a fail-safe control circuit that is operative to disable the robot in the event of a machine fault condition.
II. Discussion of the Prior Art
In U.S. Pat. No. 4,976,582 to Raymond Clavel (the Clavel '582 patent), there is described a robot for handling products in a three-dimensional space. The teachings of that patent are hereby incorporated by reference as if fully set forth herein. Because of the three-sided geometry of the mechanism, the device in the Clavel '582 patent has become known in the industry as a Delta Robot and that terminology will be used herein. The robot of the type described therein is designed for high-speed and high-accuracy pick-and-place applications, such as may be effectively used in the packaging machine industry, for picking products from a conveyor belt and placing them in cartons or to the infeed of a high-speed wrapping machine with a predetermined orientation and spacing between products.
Referring to FIG. 2 of the Clavel '582 patent, the Delta Robot includes a generally triangular-shaped main casting 1 having three rotatable shafts 2 journaled for rotation about horizontal axes extending generally parallel to the three sides of the triangular casting 1. Each of the three shafts is arranged to driven by a servo motor 3 for rotating the arms 4 in a vertical plane. Rotary encoders 7 on the servo motor 3 feed positional information to a main controller module 12.
At the free ends of the arms 4 are crossbars of a predetermined length dimension and carrying a detachable connector, such as ball and socket joints 26, at opposed ends thereof. The detachable ball and socket joints 26 couple the crossbars to pairs of rods or six forearms 5, all of equal length. Suspended from the lower ends of the six forearms 5 is a triangular shaped base plate member 8. More particularly, cross rods project laterally from the base plate 8 proximate the three vertices thereof and detachable connectors, e.g., ball and socket joints 27, are used to join the lower ends of the forearm members 5 to the cross rods.
Supported from the underside of the base plate 8 is an end effector 9 which may comprise a vacuum cup or other type of gripping member. In that the forearms 5 are of equal length, as the respective servo motors impart rotation to the arms 4, the base plate 8 carrying the end effector 9 undergoes pure translation without rotation in first swinging to pick up a product located in a first area and transporting it to a second area for release. Occasionally, inertial forces or impact forces occurring when the end effector hits a product can result in disengagement of one or more of the ball-joint connections 27 between the forearms 50 and the base plate 8. When this occurs, the base plate and end effector move in an uncontrolled manner, which can cause damage to the end effector itself or to products being handled. It is, therefore, desirable to provide a protection or safety feature to the robot to prevent damage to the machine or the products being handled in those instances where one or more of the ball or socket joints 27 become detached. The present invention provides such protection.